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Groups > comp.lang.c > #149302

Re: C String terminator

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: C String terminator
Date 2020-01-21 04:00 -0800
Organization A noiseless patient Spider
Message-ID <865zh5j9yq.fsf@linuxsc.com> (permalink)
References <qvktc8$gvf$1@dont-email.me> <303beb4a-dd99-4dbd-bbb7-eb8a07632526@googlegroups.com> <87imlcimc8.fsf@nosuchdomain.example.com> <874kwwf9cs.fsf@bsb.me.uk> <qvsrol$10f5$1@gioia.aioe.org>

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Manfred <noname@add.invalid> writes:

> On 1/16/2020 3:01 AM, Ben Bacarisse wrote:
>
>>> printf() and other C string handling functions have undefined behavior
>>> if passed a pointer that doesn't point to a string.
>>
>> To be a bit picky...  Given
>>
>>    char a[3] = "foo", b[3] = "bar";  // neither is null-terminated.
>>
>> a call like
>>
>>    strncmp(a, b, sizeof a)
>>   is not undefined even though the standard calls strncmp a string
>> handling function.  The description takes care to talk about character
>> arrays, though.
>>
>> Calls like
>>
>>    strcmp(a, b)
>>    strchr(a, 'o')
>>    strspn(b, "abc")
>>
>> would, from an operational point of view, seem to be well-defined as the
>> presence of a null is not obviously needed, but the function
>> descriptions say the pointers should point to strings.  Are they
>> undefined calls?
>
> Since the standard requires these functions to be called with (null
> terminated) strings, I would say that these are formally UB calls,
> even if any sane implementation will give the correct result (which
> also falls within the category of UB).

The phrasing there seems a bit off.  "Undefined behavior" is a
semantic specification.  The result -- or any result -- of a
computation cannot be "undefined behavior".  What I think you mean
is that giving an expected result is allowed when the construct in
question is specified as having undefined behavior.

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Thread

C String terminator T <T@invalid.invalid> - 2020-01-14 09:22 -0800
  Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-14 09:32 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-14 09:43 -0800
      Re: C String terminator Bart <bc@freeuk.com> - 2020-01-14 17:53 +0000
        Re: C String terminator David Brown <david.brown@hesbynett.no> - 2020-01-14 20:17 +0100
          Re: C String terminator Bart <bc@freeuk.com> - 2020-01-14 20:01 +0000
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-14 09:57 -0800
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 11:37 -0800
          Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:02 -0800
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:38 -0800
              Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:53 -0800
        Re: C String terminator Manfred <noname@add.invalid> - 2020-01-14 20:48 +0100
    Re: C String terminator chad <cdalten@gmail.com> - 2020-01-15 05:43 -0800
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 07:12 -0800
      Re: C String terminator Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-15 15:35 +0000
        Re: C String terminator chad <cdalten@gmail.com> - 2020-01-19 06:20 -0800
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 10:52 -0800
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 12:52 -0800
        Re: C String terminator gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-15 20:56 +0000
        Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 02:17 +0000
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 21:54 -0800
          Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-16 02:07 -0800
            Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-16 02:45 -0800
              Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-16 08:21 -0700
                Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-16 08:03 -0800
              Re: C String terminator John Bode <jfbode1029@gmail.com> - 2020-01-16 09:06 -0800
              Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-16 11:29 -0800
      Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 02:01 +0000
        Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-15 23:02 -0500
        Re: C String terminator David Brown <david.brown@hesbynett.no> - 2020-01-16 11:15 +0100
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 13:07 +0000
        Re: C String terminator Manfred <noname@add.invalid> - 2020-01-17 18:43 +0100
          Re: C String terminator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-21 04:00 -0800
          Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-21 05:00 -0800
  Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-14 12:36 -0700
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 12:05 -0800
      Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-14 13:54 -0700
        Re: C String terminator James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-14 15:03 -0800
          Re: C String terminator Thiago Adams <thiago.adams@gmail.com> - 2020-01-15 04:55 -0800
            Re: C String terminator Guillaume <message@bottle.org> - 2020-01-15 20:49 +0100
              Re: C String terminator Thiago Adams <thiago.adams@gmail.com> - 2020-01-15 12:55 -0800
        Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-14 21:31 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:28 -0800
      Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:38 -0800
        Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-15 10:50 -0700
          Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:17 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:53 -0800
  Re: C String terminator Richard Damon <Richard@Damon-Family.org> - 2020-01-14 21:43 -0500
  Re: C String terminator "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-14 22:52 -0800
    Re: C String terminator "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2020-01-14 22:54 -0800
  Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 02:00 -0800
    Re: C String terminator gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-15 10:47 +0000
      Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-15 03:02 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:19 -0800
      Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 11:33 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 12:03 -0800
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 01:30 +0000
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 18:17 -0800
              Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 03:44 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 20:33 -0800
          Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-16 02:26 -0800
  Re: C String terminator Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-15 15:11 +0000
    Re: C String terminator T <T@invalid.invalid> - 2020-01-15 09:32 -0800
      Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 10:47 -0800
        Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:58 -0800
          Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 01:39 +0000
            Re: C String terminator T <T@invalid.invalid> - 2020-01-15 18:27 -0800
              Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:03 -0800
              Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 03:28 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:33 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-15 19:38 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 13:31 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 09:09 -0800
                Re: C String terminator Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-01-16 10:27 -0700
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 10:54 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:59 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:11 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:17 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:14 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 23:45 +0000
                Yes, Ben makes house calls (Was: C String terminator) gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-16 23:57 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 11:28 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-17 20:46 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 12:48 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 12:54 -0800
                Re: C String terminator Bart <bc@freeuk.com> - 2020-01-17 21:02 +0000
                Re: C String terminator Bart <bc@freeuk.com> - 2020-01-17 21:21 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:35 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:44 -0800
                Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-17 15:03 -0800
                Re: C String terminator fir <profesor.fir@gmail.com> - 2020-01-17 15:06 -0800
                Re: C String terminator Ike Naar <ike@sdf.lonestar.org> - 2020-01-18 07:30 +0000
                Re: C String terminator Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-01-17 16:06 -0500
                Re: C String terminator Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-01-17 16:23 -0500
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 13:37 -0800
                Re: C String terminator Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-21 04:10 -0800
                Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-21 10:41 -0800
                Re: C String terminator Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-01-17 01:55 -0800
                Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-17 09:52 -0800
                Re: C String terminator T <T@invalid.invalid> - 2020-01-17 11:29 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 18:21 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 10:50 -0800
                Re: C String terminator Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-16 20:50 +0000
                Re: C String terminator T <T@invalid.invalid> - 2020-01-16 14:17 -0800
  Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-15 09:59 -0800
  Re: C String terminator T <T@invalid.invalid> - 2020-01-15 10:15 -0800
  Re: C String terminator T <T@invalid.invalid> - 2020-01-18 21:42 -0800
    Re: C String terminator T <T@invalid.invalid> - 2020-01-19 22:13 -0800
  Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-21 19:49 +0100
  Re: C String terminator John Bode <jfbode1029@gmail.com> - 2020-01-21 15:33 -0800
    Re: C String terminator Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-21 23:19 -0800
    Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-22 08:39 +0100
      Re: C String terminator chad <cdalten@gmail.com> - 2020-01-22 06:59 -0800
        Re: C String terminator Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-22 18:44 +0100

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